Synergistic Enhancement of Thermoelectric Performance in n-Type Mg ₃ Sb ₂ via a Stepwise Magnesium Compensation Strategy and Bismuth Doping

While the melting method is promising for scalable production of Zintl-phase thermoelectrics, fabricating n-type Mg3Sb2 via this route remains challenging due to severe Mg volatilization. Building upon the concept of stepwise Mg compensation, this study introduces a key optimization: the symmetrical placement of Mg chips on both surfaces of the pellet during spark plasma sintering, as opposed to single-side compensation. This designed double-sided compensation strategy proves critical in achieving uniform and sufficient Mg supplementation throughout the bulk material. Combined with Bi doping at Sb sites to synergistically enhance phonon scattering and modify electronic transport, this approach yields exceptional thermoelectric performance. The optimized composition, Mg3.9(Sb0.75Bi0.25)1.99Te0.01 with 14 wt % Mg compensation, achieves a peak ZT value of 1.19 at 723 K. Our work validates that the symmetrical stepwise compensation strategy is a robust and effective route for realizing high-performance n-type Mg3Sb2-based materials via the melting method.